1. Field of the Invention
The present general inventive concept relates to an image forming apparatus and a control method thereof, and more particularly, to an image forming apparatus which can detect malfunction of a switching unit or relay unit and a control method thereof.
2. Description of the Related Art
A conventional image forming apparatus that uses an electrophotographic method includes a fixing unit that fixes an image transferred on a printing medium. The fixing unit includes a heating roller, a pressurization roller and a lamp. Therefore, a surface of the heating roller is heated by heat emitted from the lamp, and the image transferred on the printing medium is fixed to the printing medium by mutual compression between the pressurization roller and the heating roller.
The conventional image forming apparatus using the electrophotographic method generally uses a triac (TRIode for Alternating Current; TRIAC) to supply an operating voltage to the lamp. Since more heat is needed in a high speed device than a low speed device, more electric current flows through the triac. Accordingly, the heat generated from the triac is increased and thus raises a temperature of the triac. However, a triac thermal runaway feature of a continuous ON state regardless of an external control signal occurs at temperatures higher than about 120°.
If a heat radiating plate for the triac is designed to be large to radiate the heat, the thermal runaway can be prevented beforehand, but frequently a spatial restriction etc., does not allow an enough margin. If the heat is not radiated properly, the triac keeps the ON state continuously regardless of the external control signal, and the lamp of the fixing unit is continuously supplied with the operating voltage. As a result, the temperature of the triac continues to ascend. Therefore, the fixing unit may be damaged due to the heat from high temperature or other problems may occur due to the temperature rise of the triac.